The present invention relates in general to a device for separating of a liquid, especially whole blood, into fractions having different densities. More particularly, the invention relates to a device comprising a rotatable separation unit having inlet means to be connected to a source for the liquid to be separated and outlet means to be connected to collection points for the separated fractions.
U.S. Pat. No. 4,007,871 discloses a separation unit for use in a device to separate whole blood into fractions according to their respective densities. The separation unit according to this patent is formed of two circular sheets of flexible material, which are joined together to provide a generally annular separation chamber therebetween. An inlet tube is welded between the sheets to provide inlet means into said chamber for the liquid to be separated, and several outlet tubes are similarly welded between the sheets to provide outlet means for each of the separated fractions from a common collection portion of the separation chamber.
U.S. Pat. No. 4,010,894 relates to a similar separation unit. The main difference between the two separation units is that the separation chamber disclosed in the '894 patent is extended by an outer annular separation chamber in fluid communication with an inner separation chamber by means of a radial connecting channel. Even this separation unit, however, comprises two circular sheets of flexible material and several tubes welded between the two sheets.
A major disadvantage of these two known separation units is that mixing of the separated fractions may occur in the separation chamber due to the fact that the same collection portion is used to collect more than one fraction. Another disadvantage is the use of a great number of individual components (two sheets and at least three separate tubes), whereby inner as well as outer leakages may occur due to insufficient sealing (welding). In addition, the separation units may rupture as a result of an asymmetric liquid distribution in the separation chamber. The main reason for this is that the two sheets used in the device are formed of flexible material, as suggested on lines 20-23 in column 3 of U.S. Pat. No. 4,007,871.